3D NAND Etch

ABSTRACT

Methods of etching film stacks to form gaps of uniform width are described. A film stack is etched through a hardmask. A conformal liner is deposited in the gap. The bottom of the liner is removed. The film stack is selectively etched relative to the liner. The liner is removed. The method may be repeated to a predetermined depth.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/523,262, filed Jul. 26, 2019 which claims priority to U.S.Provisional Application No. 62/743,877, filed Oct. 10, 2018, and U.S.Provisional Application No. 62/711,285, filed Jul. 27, 2018, the entiredisclosures of which are hereby incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the disclosure generally relate to etch methods forforming a gap or feature in a semiconductor device. More specifically,embodiments of the disclosure relate to etch methods for formingwordlines in three dimensional semiconductor devices.

BACKGROUND

Semiconductor and electronics processing industries continue to strivefor larger production yields while increasing the uniformity of layersdeposited on substrates having larger surface areas. These same factorsin combination with new materials also provide higher integration ofcircuits per area of the substrate. As circuit integration increases,the need for greater uniformity and process control regarding layerthickness rises. As a result, various technologies have been developedto deposit and etch layers on substrates in a cost-effective manner,while maintaining control over the physical and chemical characteristicsof the layer.

V-NAND, or 3D-NAND, structures are used in flash memory applications.V-NAND devices are vertically stacked NAND structures with a largenumber of cells arranged in blocks. Prior to wordline formation, thesubstrate is a layered oxide stack. A memory string is formed in a gapor slit that passes vertically through the layered oxide stack.

Generally, formation of a 3D NAND structure requires etching a straightprofile within a film stack. However, current etch processes,particularly with thicker film stacks, damage the sidewalls of theetched gap to provide sidewalls which are bowed in the middle of thefilm stack. These gaps are not of uniform thickness and may providevarying resistance when the gap is later filled with a conductivematerial.

Formation of a gap of uniform thickness is challenging due to theloading effect of the etch process. Current etch processes often damagethe sidewall of the gap during etching of thick stacks, resulting in anon-uniform gap thickness at the top of the stack than at the middle orbottom. This difference often becomes more pronounced with increasingoxide stack layers.

Therefore, there is a need in the art for methods for forming wordlinegaps of uniform thickness in three-dimensional structured devices.

SUMMARY

One or more embodiments of the disclosure are directed to methods ofetching a film stack. The methods comprise providing a substrate with afilm stack of a first thickness formed thereon. The film stack is etchedto a depth of a second thickness to form a gap of substantially uniformwidth with a sidewall and a bottom. The second thickness is less thanthe first thickness. A liner is deposited on the sidewall and the bottomof the gap. The liner is etched from the bottom of the gap. The filmstack is selectively etched relative to the liner to a depth of a thirdthickness to extend a depth of the gap. The liner is removed.

Additional embodiments of the disclosure are also directed to methods ofetching a film stack. The methods comprise providing a substrate with afilm stack of a first thickness formed thereon. The film stack comprisesalternating layers of an oxide and a nitride. A patterned hardmask isformed on the film stack. The film stack is etched through the hardmaskto a depth of a second thickness to form a gap of substantially uniformwidth with a sidewall and a bottom. The second thickness is less thanthe first thickness. A conformal liner is deposited by atomic layerdeposition on the sidewall and the bottom of the gap. The conformalliner comprises boron. The liner is etched from the bottom of the gap.The film stack is selectively etched relative to the liner to a depth ofa third thickness to extend a depth of the gap. An anneal of thesubstrate is performed under an oxidizing atmosphere to remove theliner.

Further embodiments of the disclosure are directed to methods of etchinga film stack. The methods comprise providing a substrate with a filmstack formed thereon of a first thickness in a range of about 3000 nm toabout 7000 nm. The film stack comprises alternating layers of an oxideand a nitride. A patterned hardmask is formed on the film stack withopenings exposing the film stack. The openings have a width in a rangeof about 1 nm to about 100 nm. The film stack is etched through thehardmask to a depth of a second thickness to form a gap of substantiallyuniform width with a sidewall and a bottom. The second thickness is lessthan the first thickness. A substantially conformal liner is depositedby atomic layer deposition on the sidewall and the bottom of the gap.The conformal liner comprises boron and carbon. The liner is etched fromthe bottom of the gap. The film stack is selectively etched relative tothe liner to a depth of a third thickness to extend a depth of the gap.The liner is removed by a process comprising an anneal under a steamatmosphere at a temperature greater than or equal to about 500° C. andan oxygen plasma ash at a temperature in a range of about 300° C. toabout 400° C.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments. The embodiments as described herein areillustrated by way of example and not limitation in the FIGURES of theaccompanying drawings in which like references indicate similarelements.

The FIGURE depicts a flow process diagram of a method of etching a filmstack according to one or more embodiments described herein.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the disclosure, it isto be understood that the disclosure is not limited to the details ofconstruction or process steps set forth in the following description.The disclosure is capable of other embodiments and of being practiced orbeing carried out in various ways.

As used in this specification and the appended claims, the term“substrate” refers to a surface, or portion of a surface, upon which aprocess acts. It will also be understood by those skilled in the artthat reference to a substrate can refer to only a portion of thesubstrate, unless the context clearly indicates otherwise. Additionally,reference to depositing on a substrate can mean both a bare substrateand a substrate with one or more films or features deposited or formedthereon.

A “substrate” as used herein, refers to any substrate or materialsurface formed on a substrate upon which film processing is performedduring a fabrication process. For example, a substrate surface on whichprocessing can be performed include materials such as silicon, siliconoxide, strained silicon, silicon on insulator (SOI), carbon dopedsilicon oxides, amorphous silicon, doped silicon, germanium, galliumarsenide, glass, sapphire, and any other materials such as metals, metalnitrides, metal alloys, and other conductive materials, depending on theapplication. Substrates include, without limitation, semiconductorwafers. Substrates may be exposed to a pretreatment process to polish,etch, reduce, oxidize, hydroxylate (or otherwise generate or grafttarget chemical moieties to impart chemical functionality), annealand/or bake the substrate surface. In addition to processing directly onthe surface of the substrate itself, in the present disclosure, any ofthe film processing steps disclosed may also be performed on anunderlayer formed on the substrate as disclosed in more detail below,and the term “substrate surface” is intended to include such underlayeras the context indicates. Thus for example, where a film/layer orpartial film/layer has been deposited onto a substrate surface, theexposed surface of the newly deposited film/layer becomes the substratesurface. What a given substrate surface comprises will depend on whatmaterials are to be deposited, as well as the particular chemistry used.

As used in this specification and the appended claims, the terms“precursor”, “reactant”, “reactive gas” and the like are usedinterchangeably to refer to any gaseous species that can react with thesubstrate surface.

“Atomic layer deposition” or “cyclical deposition” as used herein refersto the sequential exposure of two or more reactive compounds to deposita layer of material on a substrate surface. The substrate, or portion ofthe substrate, is exposed separately to the two or more reactivecompounds which are introduced into a reaction zone of a processingchamber. In a time-domain ALD process, exposure to each reactivecompound is separated by a time delay to allow each compound to adhereand/or react on the substrate surface and then be purged from theprocessing chamber. These reactive compounds are said to be exposed tothe substrate sequentially. In a spatial ALD process, different portionsof the substrate surface, or material on the substrate surface, areexposed simultaneously to the two or more reactive compounds so that anygiven point on the substrate is substantially not exposed to more thanone reactive compound simultaneously. As used in this specification andthe appended claims, the term “substantially” used in this respectmeans, as will be understood by those skilled in the art, that there isthe possibility that a small portion of the substrate may be exposed tomultiple reactive gases simultaneously due to diffusion, and that thesimultaneous exposure is unintended.

In one aspect of a time-domain ALD process, a first reactive gas (i.e.,a first precursor or compound A) is pulsed into the reaction zonefollowed by a first time delay. Next, a second precursor or compound Bis pulsed into the reaction zone followed by a second delay. During eachtime delay, a purge gas, such as argon, is introduced into theprocessing chamber to purge the reaction zone or otherwise remove anyresidual reactive compound or reaction by-products from the reactionzone. Alternatively, the purge gas may flow continuously throughout thedeposition process so that only the purge gas flows during the timedelay between pulses of reactive compounds. The reactive compounds arealternatively pulsed until a desired film or film thickness is formed onthe substrate surface. In either scenario, the ALD process of pulsingcompound A, purge gas, compound B and purge gas is a cycle. A cycle canstart with either compound A or compound B and continue the respectiveorder of the cycle until achieving a film with the predeterminedthickness.

In an embodiment of a spatial ALD process, a first reactive gas andsecond reactive gas (e.g., nitrogen gas) are delivered simultaneously tothe reaction zone but are separated by an inert gas curtain and/or avacuum curtain. The substrate is moved relative to the gas deliveryapparatus so that any given point on the substrate is exposed to thefirst reactive gas and the second reactive gas.

Embodiments of the disclosure advantageously provide methods of etchingfilm stacks which provide gaps of uniform width. Without being bound bytheory, it is believed that the use of shallower etches and protectiveliners provides for processes with less sidewall damage and gaps of moreuniform width through the film stack.

As used herein, a gap of “substantially uniform” width refers to a gapwhere the width is about the same throughout (e.g., at the top, middleand bottom of the gap). Without being bound by theory, it is assumedthat a gap of exactly uniform width will be more difficult to achieve.Therefore, a gap of substantially uniform width is a gap where the widthvaries by less than or equal to about 10%, 5%, 2%, 1% or 0.5%.

As used herein, a liner which is “substantially conformal” refers to aliner where the thickness is about the same throughout (e.g., on thetop, middle and bottom of sidewalls and on the bottom of the gap). Aliner which is substantially conformal varies in thickness by less thanor equal to about 10%, 5%, 2%, 1% or 0.5%.

As used herein, a etch process which is “substantially directional”refers to a process which removes quantities of a material in onedirection over another direction (e.g., removes a vertical trench from afilm stack, without etching the sidewalls of the trench). A processwhich is substantially directional preferentially removes material in afirst direction at a rate that is 10, 20, 50 or 100 times faster thanmaterial removed in a second direction orthogonal to the first.

The FIGURE depicts a flow diagram of a method 100 of etching a filmstack in accordance with one or more embodiments of the disclosure. Withreference to the FIGURE, the method 100 begins with a substrate 210 witha film stack 220 formed thereon. The film stack 220 is comprised ofmultiple layers 220 a, 220 b. In some embodiments, the multiple layers220 a, 220 b alternate in the film stack 220. In some embodiments, thefilm stack 220 comprises more than two alternating layers. In someembodiments, the film stack 220 comprises a number of layers in a rangeof about 2 layers to about 500 layers, in a range of about 20 layers toabout 200 layers, in a range of about 50 layers to about 150 layers, ina range of about 80 layers to about 150 layers, or in a range of about100 layers to about 120 layers.

The film stack 220 formed on the substrate 210 has a thickness D1, alsoreferred to as a first thickness. In some embodiments, the firstthickness is in a range of about 3000 nm to about 7000 nm. Each of theindividual layers has an individual thickness. In some embodiments, theindividual thickness is in a range of about 100 Å to about 3000 Å, about100 Å to about 500 Å, or in a range of about 500 Å to about 3000 Å.

In some embodiments, the film stack 220 comprises alternating layers ofan oxide and a nitride. In some embodiments, the film stack 220comprises alternating layers of an oxide and a polysilicon stack.

In some embodiments, at operation 110, a patterned hardmask 230 isformed on the film stack 220. The patterned hardmask 230 may be formedby any suitable process. In some embodiments, the patterned hardmask 230is formed as a blanket hardmask and subsequently etched to form apatterned hardmask 230. In some embodiments, the patterned hardmask 230is deposited as a hardmask with a pattern (e.g., patterned printing). Insome embodiments, operation 110 is not performed and the method 100begins with the patterned hardmask 230 on the film stack 220.

The patterned hardmask 230 has openings 235 which expose portions of thefilm stack 220. In some embodiments, the openings 235 have a width in arange of about 1 nm to about 100 nm, about 2 nm to about 80 nm, about 3nm to about 75 nm, about 4 nm to about 50 nm, or about 5 nm to about 50nm.

At operation 120, the film stack 220 is etched to a depth of a secondthickness, D2. The second thickness D2 is less than the first thicknessD1. Stated differently, the etch process at operation 120 does not etchthe entire film stack 220. The etch process at operation 120 forms a gap240. The gap 240 has at least one sidewall 242 and a bottom 245. The gap240 has a width W that is substantially uniform.

At operation 130, a liner 250 is deposited on the at least one sidewall242 and the bottom 245 of the gap 240. In some embodiments, the liner250 comprises boron (B). In some embodiments, the liner 250 furthercomprises nitrogen (N) or carbon (C). In some embodiments, the liner 250comprises one or more of boron, boron nitride (BN), boron carbide (BC)or boron carbonitride (BCN).

At operation 130, the liner may be deposited by any suitable process. Insome embodiments, the liner 250 is deposited by atomic layer deposition(ALD). In some embodiments, the liner is deposited by chemical vapordeposition (CVD).

“Atomic layer deposition” or “cyclical deposition” as used herein refersto the sequential exposure of two or more reactive compounds to deposita layer of material on a substrate surface. The substrate, or portion ofthe substrate, is exposed separately to the two or more reactivecompounds which are introduced into a reaction zone of a processingchamber. In a time-domain ALD process, exposure to each reactivecompound is separated by a time delay to allow each compound to adhereand/or react on the substrate surface and then be purged from theprocessing chamber. These reactive compounds are said to be exposed tothe substrate sequentially. In a spatial ALD process, different portionsof the substrate surface are exposed simultaneously to the two or morereactive compounds so that no given point on the substrate is exposed tomore than one reactive compound simultaneously. As used in thisspecification and the appended claims, the term “substantially” used inthis respect means, as will be understood by those skilled in the art,that there is the possibility that a small portion of the substrate maybe exposed to multiple reactive gases simultaneously due to diffusion,and that the simultaneous exposure is unintended. As used herein,“chemical vapor deposition” refers to a process in which a substratesurface is exposed to precursors and/or co-reagents simultaneously orsubstantially simultaneously. As used herein, “substantiallysimultaneously” refers to either a co-flow or where there is anintentional overlap of the precursors.

In some embodiments, the liner 250 is continuous. In some embodiments,the liner 250 is substantially conformal. In some embodiments, the liner250 is thicker on the at least one sidewall 242 of the gap 240 than thebottom 245 of the gap 240. In some embodiments, the thickness on the atleast one sidewall 242 of the gap 240 is greater than or equal to about100 percent, greater than or equal to about 110 percent, greater than orequal to about 120 percent, greater than or equal to about 125 percent,greater than or equal to about 150 percent, or greater than or equal toabout 200 percent of the thickness of the liner 250 on the bottom 245 ofthe gap 240. In some embodiments, the liner 250 has a thickness on onesidewall in a range of about 10 Å to about 50 Å. In some embodiments,the liner 250 has a thickness which is evaluated relative to the widthof the opening 235. In some embodiments, the liner 250 has a thicknesson opposite sidewalls of the gap 240 which comprises less than or equalto about 50%, less than or equal to about 30%, less than or equal toabout 25%, less than or equal to about 20%, or less than or equal toabout 10% of the total width of the opening 235.

At operation 140, the liner 250 is etched from the bottom 245 of the gap240 to expose the film stack 220.

At operation 150, the film stack 220 is selectively etched relative tothe liner 250 to a depth of a third thickness D3. Etching the film stack220 at 150 extends the total depth of the gap 240.

In some embodiments, the sum of second thickness D2 and the thirdthickness D3 is less than the first thickness D1. Stated differently,the etch process at operation 150 does not etch the entire film stack220. In some embodiments, operations 130 140 and 150 may be repeateduntil a predetermined thickness has been etched from the film stack 220.

As used herein, the phrase “selectively etched”, or similar, means thatthe subject materials are etched to a greater extent than othermaterials. In some embodiments, “selectively” means that the subjectmaterial is removed at a rate greater than or equal to about 10×, 15×,20×, 25×, 30×, 35×, 40×, 45× or 50× the rate of removal from thenon-selected surface. Without being bound by theory, it is believed thatthe liner 250 protects the at least one sidewall 242 of the gap 240during operation 150, enabling the selective etching of the film stack.

In some embodiments, not illustrated, after operation 150, the liner 250is removed from the at least one sidewall 242. In some embodiments, theliner 250 is removed by a process comprising an anneal in an oxidizingatmosphere. In some embodiments, the oxidizing atmosphere comprises oneor more of O₂, O₃, H₂O, H₂O₂, CO, CO₂, N₂O, NO₂ or NO. In someembodiments, the anneal is performed at a temperature greater than orequal to about 450° C., greater than or equal to about 500° C., greaterthan or equal to about 600° C., greater than or equal to about 750° C.,greater than or equal to about 1000° C., greater than or equal to about1100° C., or greater than or equal to about 1200° C. In someembodiments, the liner is removed by a process comprising a waterplasma. In some embodiments, the liner is removed by a processcomprising an oxygen plasma ash. In some embodiments, the oxygen plasmaash is performed at a temperature in a range of about 300° C. to about400° C.

Without being bound by theory, it is believed that for liners comprisingboron, the boron can be removed by the steam anneal process. Further,for liners comprising carbon, the carbon can be removed by the oxygenplasma ash process.

Operations 120 and 150 each involve etching the film stack 220.Operation 140 involves etching the bottom of the liner 250. The etchprocess used in operations 120, 140 and 150 may be any suitable etchprocesses. The etch process used in operation 150 may be any suitableetch processes that is selective to the film stack 220 over the liner250. In some embodiments, the etch process in operation 120 issubstantially directional. In some embodiments, the etch process inoperation 140 is substantially directional. In some embodiments, theetch process in operation 150 is substantially directional. In someembodiments, the etch processes utilized in operations 120 and 150 aresimilar processes. In some embodiments, the etch process utilized inoperation 140 is different from either the etch process utilized inoperation 120 or the etch process utilized in operation 150. As used inthis regard, similar etch processes are performed using the samereagents under the same conditions. A skilled artisan will appreciatethat the conditions may vary slightly between similar processes and suchvariations are within the scope of the disclosure.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the disclosure herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present disclosure without departing from the spiritand scope of the disclosure. Thus, it is intended that the presentdisclosure include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A method of etching a film stack, the methodcomprising: etching a film stack having a first thickness to a depth ofa second thickness to form a gap with a substantially uniform width, asidewall and a bottom, the second thickness being less than the firstthickness; depositing a liner comprising boron on the sidewall and thebottom of the gap; etching the liner from the bottom of the gap;selectively etching the film stack relative to the liner to a depth of athird thickness to extend a depth of the gap; and removing the liner. 2.The method of claim 1, wherein the film stack comprises alternatinglayers.
 3. The method of claim 2, wherein each alternating layer has athickness in a range of 100 Å to 3000 Å.
 4. The method of claim 2,wherein the alternating layers comprise an oxide layer and a nitridelayer.
 5. The method of claim 2, wherein the alternating layers comprisean oxide layer and a polysilicon stack.
 6. The method of claim 1,further comprising forming a patterned hardmask on the film stack beforeetching, and wherein openings in the patterned hardmask expose portionsof the film stack to be etched.
 7. The method of claim 1, wherein thegap has a width in a range of about 1 nm to about 100 nm.
 8. The methodof claim 1, wherein the liner comprises one or more of B, BN, BC, orBCN.
 9. The method of claim 1, wherein the liner is substantiallyconformal and deposited by atomic layer deposition.
 10. The method ofclaim 1, wherein the liner has a thickness in a range of about 10 Å toabout 50 Å.
 11. The method of claim 1, wherein the liner has a totalthickness on the sidewalls of the gap which is less than or equal to 50%of the width of the gap.
 12. The method of claim 1, wherein the linerhas a thickness on the sidewall of the gap that is greater than athickness on the bottom of the gap.
 13. The method of claim 11, whereinthe thickness of the sidewall of the gap is greater than or equal to 120percent of the thickness on the bottom of the gap.
 14. The method ofclaim 1, wherein the liner is removed by a process comprising an annealin an oxidizing atmosphere.
 15. The method of claim 10, wherein theanneal is performed at a temperature greater than or equal to about 500°C.
 16. The method of claim 1, wherein the liner further comprises carbonand the liner is removed by a process further comprising an oxygenplasma ash.
 17. The method of claim 12, wherein the oxygen plasma ash isperformed at a temperature in a range of about 300° C. to about 400° C.18. The method of claim 1, wherein each etch process is substantiallydirectional.